1. Field of the Invention
The general field of the invention is that of gyrometry, in other words the field of the measurement of rotation speeds. More precisely, the technical field of the invention is that of matter-wave rate gyros. In these gyros, the measurement of the speed relies on the measurement of the phase shift Δφ induced by the Sagnac effect between two counter-rotating matter waves in a reference frame rotating at the angular velocity {dot over (θ)}, Δφ being given by:
      Δ    ⁢                  ⁢    φ    =                    4        ⁢        Am            ℏ        ⁢                  θ        ,            .      where A is the area contained by the interferometer, in the mass of the atoms and h=2πh is Planck's constant. The exploitation of the atom Sagnac effect described hereinabove represents a technological breakthrough in the field of rate gyroscopes, which conventionally use the optical Sagnac effect, since the ratio between the atomic and optical Sagnac phase-shifts is given, all other things being equal, by the quantity mc2/(hv) and is of the order of 1010 or 1011 depending on the type of atom and the optical frequency ν in question.
2. Description of the Prior Art
The best rate gyros currently commercially available are based on the optical Sagnac effect, which takes place either in an active laser cavity or in a passive fiber interferometer. In the first case, the products are known as gyrolasers and, in the second, fiber-optic rate gyros. The replacement of the optical waves by matter waves leads to a huge gain in sensitivity, even if the latter is, in part, counterbalanced by the reduction in the signal-to-noise ratio and in the area of the interferometer. Matter-wave rate gyros have been an experimental reality since 1997, the date of the first measurement of the Earth's rotation with this type of device. Reference will be made to the article by T. Gustayson et al., Phys. Rev. Lett. 78 (1997) on this point. Today, several laboratories have constructed similar sensors, and the performances attained already surpass those of the best optical rate gyros (see D. Durfee et al., Phys. Rev. Lett. 97, 240801 (2006)). For future developments, the potential for improvement is still several orders of magnitude.
Atom rate gyros rely on the use of matter waves. According to the laws of quantum mechanics, the latter are associated with any particle that has mass. The technique of atom interferometry allows phase differences between packets of matter waves to be measured. It requires, in particular, the prior cooling of the atoms to temperatures close to absolute zero, in order to limit their thermal velocity dispersion. In the following part of the text, these cooled atoms will be called cold or ultracold atoms.
Significant efforts have been deployed in recent years in order to integrate part of the functions for trapping, cooling and manipulating cold atoms onto devices of the “chip” type, the latter having the advantage of compactness, but also of a very good control of the magnetic fields necessary for the system and of a relatively low electrical power consumption. In addition, the advantage of using and of incorporating radiofrequency fields for the coherent manipulation of the atoms, underlined in 2000 in an article by O. Zobay and B. Garraway, Two-Dimensional Atom Trapping in Field-Induced Adiabatic Potentials, Physical Review Letters 86, pages 1195-1198 (2001), has recently been experimentally demonstrated by the coherent separation into two equal parts of a Bose-Einstein condensate in 2006, which constitutes the atom equivalent of a separator plate for a laser, a key component for the construction of atom interferometers. For further information, reference will be made to the publication by T. Schumm et al., Matter-wave interferometry in a double well on an atom chip, Nature Physics 1, pages 57-62 (2005).